Juliet is almost a dream restaurant. The dishes hew lovingly and skillfully to classic Mediterranean lines, the flavors are generous, the technique is deft, the ingredients are impeccably sourced. The couple at the center of it—Joshua Lewin, a chef whose work I’ve long followed with interest and admiration, and his partner, Katrina Jazayeri—have charm and finesse in abundance. So why do I say, “almost”? Because the same homespun quality that gives this little Union Square spot its appeal could be holding it back from greatness.

Juliet may be Lewin and Jazayeri’s first brick-and-mortar venture, but the space has long been significant to the couple. When 257 Washington Street was the Sherman Café, the two would meet there often to talk about what their own dream restaurant would look and feel like, and how they could turn that dream into reality. Their opportunity came soon enough. When the Sherman closed in 2014, its owners reached out to the two regulars. Once they assumed ownership of the space, the couple tore down walls to expose a small kitchen, but—as the neighborhood happily discovered when they opened in February—they maintained the café’s airy, open interior and its welcoming atmosphere. Juliet has also kept some of the improvisatory air of the couple’s pop-up, Bread & Salt at Wink & Nod, which they ran in the South End while developing the concept for the restaurant.

Don’t be fooled by the casual vibe: They’re flexing serious culinary talent here. Lewin has the instincts to make him a natural successor to Gordon Hamersley (and yes, I realize I’m going out on a limb here). His pastas have a way with flavor that Hamersley would surely approve of—for instance, a simple plate of hen-of-the-woods mushrooms steeped in cream and butter-sautéed onions, served over egg-yolk tagliatelle ($16) that’s made by the executive sous chef who’s worked with Lewin since his time at Beacon Hill Bistro. Lewin’s meaty Bolognese ($18), livened with long-roasted, mandoline-thin lemon slices and served over the same tagliatelle, is even better. It’s a dish I could have every night, sitting at the high counter overlooking the kitchen.

Brunch, though, might be Lewin’s strongest suit. You’ll have to taste what he can do with eggs, in soft-curded omelets (starting at $9) with lemon zest and fresh fines herbes tucked in with those terrific wild mushrooms; or in a lush wedge of absolutely classic Spanish tortilla ($9).

It’s also a way for Lewin to showcase his mastery of the flavors of Provence and Spain, which sing through his puckeringly bright gazpacho ($8), garlicky and strong with tomatoes. The pulverized, oil-cured black olives he adds to the gazpacho for depth also find their way into a bread-tomato salad ($8) filled with chewy cubes of homemade olive focaccia. In addition, a lunch-menu cauliflower sandwich on an Iggy’s baguette ($9) is slathered with an unmissable fried-curry-leaf chutney that Lewin learned while staging at the cult Indian restaurant Rasika, in Washington, DC. With the generous schmears of thick chickpea spread and chutney, you need the caramelized roasted cauliflower for texture—and you’ll want more.

Lewin and Jazayeri clearly want Juliet to be a place you’ll want to come for carefully, caringly turned out dishes from morning till evening—but the very white, crisp, brightly lit interior doesn’t much lend itself to evening dining. The service, too, is much more redolent of daytime commuter takeout than a leisurely dinner. During the day, you order at the cash register and wait for food to be ferried to the table. Orders can get lost, and requests are subject to interpretation. At one Sunday brunch, my guest asked for an egg-white omelet with mushrooms on the side. They came folded into the omelet, because the chef—who came over to tell us this—thought it would be better that way. Maybe so, but definitely not what my strong-minded dining companion wanted. The person who took our orders for yogurt asked if we wanted granola, a listed option; we clearly said no, but each order came with granola anyway. Glitches are one thing at a busy brunch, but evening tableside service was a bit wobbly, too—opening pains that have persisted three and four months in. What makes this particularly unfortunate is that there are only six tables offering formal service at dinner time (part of the “chef’s table” prix fixe). Hopefully this will get ironed out, as Lewin and Jazayeri have done what I’d like to see every owner do: include service in the price of the meal, as part of a “One Fair Wage” campaign that will pay front- and back-of-house workers equitably.

Juliet’s airy interior. / Photograph by Jim Brueckner

Dinner, in fact, is where Lewin and Jazayeri most need to find their rhythm. The couple started with dinner just three nights a week: a three-course tasting menu ($55 without wine) at two evening seatings featuring a big-portioned, simple main course rounded out with flashier appetizers such as home-cured charcuterie or salmon. I was convinced by an entrée of whole roasted branzino served on a dramatically large platter with wedges of crisp, butter-baked potato mille-feuille and a simple romesco sauce with hazelnuts, tomato, and a dash of sherry vinegar. The fish was perfectly firm but not dry, though the temptingly papery skin was, disappointingly, too salty to eat. We could have easily skipped the apps, which had new-wave flourishes such as puffed rice on dry-roasted broccoli florets, in favor of the generous main course.

Desserts are a return to form—with a remarkably sure touch that would please not just Gordon Hamersley but Alice Waters. Clafouti ($7 if ordered à la carte), the very simple dessert of seasonal fruit baked in a crêpe batter, is comfort food worthy of the French grandmother you never had. A simple, dark-gold lemon tart ($7), its filling nicely grainy from sugar atop a buttery crust, was perfectly plain and perfectly right. Most Chez Panisse of all was a strawberry shortcake with just enough of those little, local, intensely perfumed strawberries—served over thin slices of a fresh, cakey biscuit—to make you curse New England’s cruelly short strawberry season.

Juliet has the ambition and skill of a destination restaurant. For breakfast and lunch—or just a civilized place to pass a sunny hour or two—it already is one. For dinner, it still needs a bit more polish to bring out the luster that the bright-eyed couple at its center will, I’m confident, burnish to a long-glowing gleam.